1. Field of the Invention
The present invention relates generally to the production of exopolysaccharides, and more specifically, to a nucleic acid sequence and variants thereof capable of modulating exopolysaccharide production, and to the use of such nucleic acid sequences to generate bacteria that hyper-produce exopolysaccharide in slime form.
2. Description of the Related Art
There is an increasing demand for inexpensive and environmentally acceptable gelling agents for industrial applications and for the food industry. Some exemplary industrial applications of gelling agents include oil field drilling, adhesives, paints, animal feed, household products, personal care products (e.g., shampoo, lotion), oral care products (e.g., toothpaste), pharmaceuticals, and the like. Some exemplary uses of gelling agents in the food industry include use in pudding, dairy products, pie filling, dressings, confectionery, sauces, syrups, and the like. The biotechnology industry has responded to this demand for gelling agents by increasing the availability of a variety of bacterial exopolysaccharide products that are acceptable for commercial use.
Bacterial exopolysaccharides are useful compounds as gelling or viscosity increasing agents because of their distinctive rheological properties (e.g., resistance to shear, compatibility with various ionic compounds, stability to extreme temperatures, pH and salt concentrations). A variety of bacteria produce exopolysaccharides particularly useful as thickening or gelling agents. For example, a genus of bacteria that produces many types of exopolysaccharides is Sphingomonas. A few such polysaccharides include gellan, welan, rhamsan, S-7, and S-88 (see, e.g., Pollock, J. Gen. Microbiol. 139:1939, 1993). The exopolysaccharides produced by Sphingomonas are referred to as “sphingans,” and at least three sphingans (gellan, welan, and rhamsan) are commercially produced by large-scale, submerged fermentation.
Many bacterial exopolysaccharide products offer a range of attractive improvements over synthetically produced materials, but they remain relatively expensive to produce because of the costs associated with recovery and purification of a desired product. Furthermore, conditions that allow for higher fermentation yields of exopolysaccharides also result in increased broth viscosity, which thickening ultimately requires higher energy input to effectively disperse oxygen and nutrients to allow sufficient bacterial growth in the fermentation broth. That is, fermentations that provide higher exopolysaccharide yields have also resulted in correspondingly higher production costs.
Hence, a need exists for a better understanding of bacterial biosynthesis of exopolysaccharide to aid in the identification of bacteria that produce more exopolysaccharide, and that produce exopolysaccharide in a form that does not increase the viscosity of a fermentation broth. In addition, a need exists for methods of making or identifying such bacteria, which in turn would allow optimization of exopolysaccharide production and yield under typical, industrial fermentation conditions. The present invention meets such needs, and further provides other related advantages.